1. Field of the Invention
The present invention relates to a compressor, and particularly, to an apparatus for controlling an operation of a reciprocating compressor and a method therefor.
2. Description of the Prior Art
In general, a reciprocating compressor linearly reciprocates an inner piston in a cylinder to inhale, compress and discharge refrigerant gas. A method for operating the piston may be divided into a recipro method and a linear method.
In the recipro method, a motor being rotated is connected to a crank shaft and the crank shaft is connected to the piston, thereby converting rotating power of the motor into a linear reciprocating motion. In the linear method, the piston is connected to an actuator of the motor which linearly moves, thereby reciprocating the piston based on the linear motion of the motor.
The reciprocating compressor to which the linear method is applied has a higher compressing efficiency than a typical compressor in the manner of the compressing efficiency, because there is not a crank shaft that converts the rotating motion into the linear motion, which results in a low friction loss.
When the reciprocating compressor is used in a refrigerator or an air conditioner, a winding wire of the motor in the reciprocating compressor is selected according to a variation value of a power supply voltage inputted in the reciprocating compressor, and thus a stroke of the compressor is controlled by applying a power to the selected winding wire. Hereinafter, the reciprocating compressor according to the related art will be explained with reference to FIG. 1.
FIG. 1 is a block diagram illustrating a construction of an apparatus for controlling an operation of the reciprocating compressor according to the Prior art.
Referring to FIG. 1, the apparatus for controlling the operation of the reciprocating compressor includes: a voltage detector 1 for detecting a voltage of an alternating current power applied to a motor (not shown) of a compressor 4; a controller 2 for comparing a voltage value detected by the voltage detector 1 with a predetermined reference voltage value, and generating a switching control signal based on the compared result; a switching portion (R1 and R2) 3 for selecting one of a high mode (L1), a normal mode (L2) and a low mode (L3) of the motor according to the switching control signal of the controller 2; a PTC (Positive Temperature Coefficient) thermistor 5 electrically connected to the motor, for cutting off over current generated at an initial operation of the reciprocating compressor, thereby protecting the reciprocating compressor 4 from being damaged; a reactor 6 connected to the PTC thermistor 5 in series; and a capacitor 7 electrically connected to the PTC thermistor 5 and the reactor 6 in parallel. The capacitor 7 countervails an inductance of a coil wound around the motor. That is, because the inductance of the coil is countervailed by the capacitor 7, a sufficient stroke can be generated even by a lower input voltage. Here, the stroke refers to a moved distance while the piston (not shown) of the reciprocating compressor 4 reciprocates.
Hereinafter, it will be explained how the apparatus for controlling the operation of the reciprocating compressor is operated.
First, the voltage detector 1 detects a voltage of an alternating current power applied to the motor of the compressor 4, and outputs the detected voltage value to the controller 2.
The controller 2 generates a switching control signal for controlling the switching portion 3 on the basis of the voltage value detected by the voltage detector 1 and a predetermined reference voltage value. That is, the controller 2 controls relays (R1 and R2) of the switching portion 3, according to a variation value of the voltage of the alternating current power applied to the motor of the compressor 4, thereby varying a voltage mode (operation mode) of the motor. For instance, if the voltage of the alternating current power provided to the reciprocating compressor 4 is identical to the predetermined reference voltage (e.g., 220 volt), the controller 2 outputs a switching control signal for converting the voltage mode of the motor installed in the reciprocating compressor 4 into the normal mode (L2). If the voltage of the alternating current power provided to the reciprocating compressor 4 exceeds the predetermined reference voltage (e.g., 240 volt), the controller 2 outputs a switching control signal for converting the voltage mode of the motor installed in the reciprocating compressor 4 into a high mode (L1). Moreover, if the voltage of the alternating current power provided to the reciprocating compressor 4 is less than the predetermined reference voltage (e.g., 200 volt), the controller 2 outputs a switching control signal for converting the voltage mode of the motor installed in the reciprocating compressor 4 into a low mode (L3). Here, the voltage mode is an operation mode to protect the motor from over voltage and operate the motor stably. That is, the voltage mode is for selecting one of motor stator coils which are divided into a first coil (L1: high mode), a second coil (L2: normal mode) and a third coil (L3: low mode), according to a varied input voltage.
Thereafter, the switching portion 3 selects one mode among the high mode, the normal mode and the low mode of the motor according to the switching control signal of the controller 2.
In order to prevent the reciprocating compressor 4 from being damaged due to over current when a power is provided to the motor of the compressor 4 at an initial state, on the other hand, the PTC thermistor 5 cuts off the over current applied to the motor of the compressor 4 at the initial operation of the compressor 4, thereby protecting the compressor 4 from overload. Here, the over current refers to current exceeding a reference current value which the motor of the compressor 4 allows. Furthermore, if a resistance value of the PTC thermistor itself is increased by the current applied to the motor of the compressor 4, the PTC thermistor 5 is turned off. At this time, the current is applied to the motor only through the capacitor 7.
However, the alternating current power applied to the compressor based on the related art may be increased or decreased at any time, and when the alternating current power is increased, the stroke of the compressor is also increased relative to the voltage of the alternating current power. At this time, if the stroke keeps increased by the variation of the alternating current power, the compressor can be damaged.
Also, the voltage of the alternating current power applied to the apparatus for controlling the operation of the compressor based on the related art is varied, the stroke of the compressor is operated irregularly due to the varied voltage, and in case that the alternating current power is varied, whenever the switching portion 3 which varies the capacity of the compressor is operated, noise can be occurred from the switching portion 3.
Meanwhile, a reciprocating compressor according to an another prior art is disclosed in U.S. Pat. No. 6,644,943 issued on 11 Nov. 2003.